Synergistic insecticidal compositions

ABSTRACT

The present invention provides a synergistic insecticidal composition comprising as essential active ingredients a neuronal sodium channel antagonist in combination with one or more compounds selected from the group consisting of pyrethroids, pyrethroid-type compounds, recombinant nucleopolyhedroviruses capable of expressing an insect toxin, organophosphates, carbamates, formamidines, macrocyclic lactones, amidinohydrazones, GABA antagonists and acetylcholine receptor ligands. 
     Also provided are methods for synergistic insect control and crop protection.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Divisional of application Ser. No. 10/145,784, filed on May 16, 2002, (pending), the entire disclosure of which is herewith incorporated by reference, which is a divisional application of application Ser. No. 09/521,987, filed on Mar. 9, 2000 (now U.S. Pat. No. 6,479,543), the entire disclosure of which is herewith incorporated by reference, which claims the benefit of provisional application Ser. No. 60/124,306 (filed Mar. 12, 1999) and Ser. No. 60/158,201 (filed on Oct. 7, 1999), the entire disclosures of which are herewith incorporated by reference.

BACKGROUND OF THE INVENTION

Insecticidal agents and compositions have been developed to control insect pests such as agrohorticultural pests, hygienic pests, or wood-eating pests and in practice have been used as a single or a mixed agent. However, economically efficient and ecologically safe insect control compositions are still being sought. Insecticidal compositions which allow for reduced effective dosage rates, increased environmental safety and lower incidence of insect resistance are highly desirable. Although the rotational application of insect control agents having different modes of action may be adopted for good pest management practice, this approach does not necessarily give satisfactory insect control. Further, even though combinations of insect control agents have been studied, a high synergistic action has not always been found. Obtaining an insecticidal composition which demonstrates no cross-resistance to existing insecticidal agents, no toxicity problems and little negative impact on the environment is extremely difficult.

Therefore, it is an object of this invention to provide a synergistic insecticidal composition which demonstrates a high controlling effect with concomitant reduced crop production cost and reduced environmental load.

It is another object of this invention to provide methods for synergistic insect control and enhanced crop protection.

SUMMARY OF THE INVENTION

The present invention provides a synergistic insecticidal composition comprising as essential active ingredients a synergistically effective amount of a neuronal sodium channel antagonist in combination with one or more compounds selected from the group consisting of pyrethroids, pyrethroid-type compounds, recombinant nucleopolyhedroviruses capable of expressing an insect toxin, organophosphates, carbamates, formamidines, macrocyclic lactones, amidinohydrazones, GABA (gamma-aminobutyric acid) antagonists, and acetylcholine receptor ligands.

The present invention also provides a method for synergistic insect control which comprises contacting said insect with a synergistically effective amount of a neuronal sodium channel antagonist in combination with one or more compounds selected from the group consisting of pyrethroids, pyrethroid-type compounds, recombinant nucleopolyhedroviruses capable of expressing an insect toxin, organophosphates, carbamates, formamidines, macrocyclic lactones, amidinohydrazones, GABA antagonists and acetylcholine receptor ligands.

The present invention further provides a method for the enhanced protection of plants from infestation and attack by insects.

DETAILED DESCRIPTION OF THE INVENTION

Definitions

“Acetylcholine receptor ligand compound” as used in this application means a compound which is capable of binding to the acetylcholine receptor site.

“Group A” as used in this application means insecticidal

-   -   1) pyrethroid compounds;     -   2) pyrethroid-type compounds;     -   3) recombinant nucleopolyhedroviruses capable of expressing an         insect toxin;     -   4) organophosphate compounds;     -   5) carbamate compounds;     -   6) formamidine compounds;     -   7) macrocyclic lactone compounds;     -   8) amidinohydrazone compounds;     -   9) GABA antagonist compounds; and     -   10) acetylcholine receptor ligand compounds.

“Haloalkyl” as used in this application means an alkyl group C_(x)H_(2x+1) having 1 to 2x+1 halogen atoms which may be the same or different, Similarly, the terms “haloalkenyl”, “haloalkynyl”, “haloalkoxy”, “halophenyl” and the like mean mono- to perhalogen substitution wherein the halogens may be the same or different.

“Halogen” as used in this application means Cl, Br, I or F.

“Neuronal sodium channel antagonist” as used in this application means a compound which is capable of preventing the ability of a neuron cell to transfer sodium ions across the cell membrane.

“Pyrethroid-type compounds” as used in this application means those compounds characterized by a non-ester linked aryl-phenoxybenzyl moiety.

“Synergism” as used in this application means a cooperative action encountered in a combination of two or more biologically active components in which the combined activity of the two or more components exceeds the sum of the activity of each component alone.

Surprisingly, it has now been found that a composition which comprises a combination of a neuronal sodium channel antagonist and a second insecticidal ingredient provides superior insect control at lower levels of the combined active agents than may be achieved when the neuronal sodium channel antagonist or the second insecticidal ingredient is applied alone.

As previously stated, the term neuronal sodium channel antagonist designates a compound which is capable of preventing the ability of a neuron cell to transfer sodium ions across the cell membrane. A neuron cell thus affected is unable to fire, resulting in paralysis, and ultimately mortality, in the target host. Descriptions of neuronal sodium channel antagonists and their mode of action may be found in Pesticide Biochemistry and Physiology, 60: 177-185 or Archives of Insect Biochemistry and Physiology, 37: 91-103.

Neuronal sodium channel antagonists include compounds such as those described in U.S. Pat. Nos. 5,543,573; 5,708,170; 5,324,837 and 5,462,938, (the description of which are hereby incorporated by reference) among other publications. Exemplary of the neuronal sodium channel antagonist compounds useful in the composition of this invention are those compounds having the structural formula

wherein A is CR₄R₅ or NR₆;

-   -   W is O or S;     -   X, Y, Z, X′, Y′ and Z′ are each independently H; halogen; OH;         CN; NO₂; C₁-C₆alkyl optionally substituted with one or more         halogen, C₁-C₃alkoxy, C₁-C₃haloalkoxy, C₃-C₆cycloalkyl,         C₂-C₆alkenyloxy or sulfonyloxy groups;         -   C₁-C₆alkoxy optionally substituted with one or more halogen,             C₁-C₃alkoxy or C₃-C₆cycloalkyl groups;         -   C₁-C₆alkoxycarbonyl, C₃-C₆cycloalkylcarbonyloxy, phenyl             optionally substituted with one or more halogen, C₁-C₄alkyl,             or C₁-C₄alkoxy groups;         -   aminocarbonyloxy optionally substituted with one or more             C₁-C₃alkyl groups;         -   C₁-C₆alkoxycarbonyloxy; C₁-C₆alkylsulfonyloxy;         -   C₂-C₆alkenyl; or NR₁₂R₁₃;     -   m, p and q are each independently an integer of 1, 2, 3, 4, or         5;     -   n is an integer of 0, 1 or 2;     -   r is an integer of 1 or 2;     -   t is an integer of 1, 2, 3 or 4;     -   R, R₁, R₂, R₃, R₄ and R₅ are each independently H or C₁-C₄alkyl;     -   R₆ is H, C₁-C₆alkyl, C₁-C₆haloalkyl, C₁-C₆alkoxyalkyl,         C₁-C₆alkoxy, C₁-C₆haloalkoxy, C₂-C₆alkenyl, C₂-C₆alkynyl,         C₁-C₆alkylcarbonyl, C₁-C₆alkoxy-carbonyl, C₁-C₆alkylthio, or         C₁-C₆haloalkylthio;     -   R₇ and R₈ are each independently H; halogen; C₁-C₆alkyl;         C₁-C₆alkylcarbonyloxy; or phenyl optionally substituted with one         or more halogen, CN, NO₂, C₁-C₆alkyl, C₂-C₆halo-alkyl,         C₁-C₆alkoxy or C₁-C₆haloalkoxy groups;     -   R₉ and R₁₀ are each independently H, or C₁-C₄alkyl;     -   R₁₁ is H, C₁-C₆alkyl, C₁-C₆haloalkyl, C₁-C₄alkyl-carbonyl,         C₁-C₆alkoxycarbonyl, or C₁-C₆halo-alkoxycarbonyl;     -   R₁₂ and R₁₃ are each independently H or C₁-C₆alkyl;     -   G is H, C₁-C₆alkyl, optionally substituted with one or more         halogen, C₁-C₄alkoxy, C₁-C₆haloalkoxy, CN, NO₂, S(O)_(u)R₁₄,         COR₁₅, CO₂R₁₆, phenyl or C₃-C₆cycloalkyl groups;         -   C₁-C₆alkoxy; C₁-C₆haloalkoxy; CN; NO₂; S(O)_(u)R₁₇;         -   COR₁₈; CO₂R₁₉; phenyl optionally substituted with one or             more halogen, CN, C₁-C₃halo-alkyl, or C₁-C₃haloalkoxy             groups;         -   C₃-C₆cycloalkyl; or phenylthio;     -   Q is phenyl optionally substituted with one or more halogen, CN,         SCN, NO₂, S(O)_(u)R₂₀, C₁-C₄alkyl, C₁-C₄haloalkyl,         C₁-C₄alkoxyalkyl, C₁-C₆alkoxy, C₁-C₆haloalkoxy, or NR₂₁R₂₂         groups;     -   u is an integer of 0, 1 or 2;     -   R₁₄, R₁₅, R₁₆, R₁₈, R₁₉, R₂₁ and R₂₂ are each independently H or         C₁-C₆alkyl;     -   R₁₇ and R₂₀ are each independently C₁-C₆alkyl or C₁-C₆haloalkyl;     -   R₃₃ is CO₂R₃₄;     -   R₃₄ is H, C₁-C₆alkyl, C₁-C₆haloalkyl, phenyl or halophenyl; and         the dotted line configuration     -   C         N represents a double bond or a single bond (i.e. C—N or C═N);         or         a stereoisomer thereof.

Preferred neuronal sodium channel antagonists suitable for use in the composition of the invention are those compounds of formula I, II or III wherein the dotted line configuration C

N represents a double bond.

More preferred neuronal sodium channel antagonists suitable for use in the inventive composition are those compounds of formula I or formula III wherein the dotted line configuration represents a double bond.

Particularly preferred neuronal sodium channel antagonists useful in the composition of the invention are those compounds of formula I or formula III wherein W is O; X is trifluoromethoxy and is in the 4-position; Y is trifluoromethyl and is in the 3-position; Z is CN and is in the 4-position; A is CH₂; n is 0; m, p and q are each 1; R and R₁ are each H; Z, is C₁; R₃₃ and G are each CO₂CH₃; Q is p-(trifluoromethoxy)phenyl; and the dotted line configuration C

N represents a double bond; or a stereoisomer thereof.

Further neuronal sodium channel antagonist compounds include those described in U.S. Pat. No. 5,116,850 and U.S. Pat. No. 5,304,573, (the description of which are hereby incorporated by reference) among other publications. Exemplary of further neuronal sodium channel antagonist compounds suitable for use in the composition of the invention are those compounds having structural formula

wherein W is O or S;

-   -   X″ and Y″ are each independently H; halogen; CN; SCN; C₁-C₆alkyl         optionally substituted with one or more halogen, NO₂, CN,         C₁-C₄alkoxy, C₁-C₄alkylthio, phenyl, halophenyl,         C₁-C₄alkylsulfonyl, C₁-C₄haloalkylsulfonyl, or         C₁-C₄alkoxycarbonyl groups;         -   C₂-C₄alkenyl; C₂-C₄haloalkenyl; C₂-C₄alkynyl;             C₂-C₄haloalkynyl; C₃-C₆cycloalkyl; C₃-C₆halocycloalkyl;             phenyl optionally substituted with one or more halogen, CN,             NO₂, C₁-C₄alkyl, C₁-C₄haloalkyl, C₁-C₄alkoxy,             C₁-C₄haloalkoxy, C₁-C₄alkylthio, C₁-C₄alkylsulfonyl or             C₁-C₄haloalkylsulfonyl groups;         -   C₁-C₄alkylcarbonyl; C₁-C₄haloalkylcarbonyl; or NR₂₈R₂₉;     -   m is an integer of 1, 2, 3, 4 or 5;     -   G′ is phenyl optionally substituted with one or more groups         which may be the same or different selected from X″;         -   a 5-membered heteroaromatic ring containing one or two             heteroatoms selected from 0 or 1 oxygen, 0 or 1 sulfur and             0, 1 or 2 nitrogen atoms said 5-membered heteroaromatic ring             being attached via carbon and being optionally substituted             with one or more groups which may be the same or different             selected from X″; or         -   a 6-membered heteroaromatic ring containing one or two             heteroatoms selected from 0 or 1 oxygen, 0 or 1 sulfur and             0, 1 or 2 nitrogen atoms said 6-membered heteroaromatic ring             being attached via carbon and being optionally substituted             with one or more groups which may be the same or different             selected from X″;     -   Q′ is H; C₁-C₆alkyl optionally substituted with one or more         halogen, CN, C₁-C₃alkoxy, C₁-C₆alkoxycarbonyl, or phenyl         optionally substituted with one or more halogen, CN, NO₂,         C₁-C₄alkyl, C₁-C₄haloalkyl, C₁-C₄alkylsulfonyl or         C₁-C₄alkylsulfinyl groups;         -   C₂-C₆alkenyl; C₂-C₆alkynyl; or phenyl optionally substituted             with one to three groups, which may be the same or             different, selected from X″;     -   R₂₃, R₂₄, R₂₅, R₂₆, R₂₇, R₂₈ and R₂₉ are each independently H or         C₁-C₄alkyl; and the dotted line configuration C         N represents a double bond or a single bond (i.e. C—N or C═N);         or         a stereoisomer thereof.

Further preferred neuronal sodium channel antagonist compounds of the invention are those compounds of formula IV or V wherein the dotted line configuration C

N represents a double bond.

Other preferred neuronal sodium channel antagonist compounds suitable for use in the composition of the invention are those compounds of formula IV or V wherein W is 0; X″ and Y″ are each independently H or C₁-C₆halo-alkyl; m is 1; R₂₃, R₂₄, R₂₅, R₂₆ and R₂₇ are each H; G′ is phenyl optionally substituted with one or more halogen atoms; Q′ is halophenyl or C₁-C₄alkyl optionally substituted with one phenyl or halophenyl group; and the dotted line configuration

represents a double bond; or a stereoisomer thereof.

The second active ingredient of the insecticidal composition of the invention includes one or more compounds selected from Group A:

1) pyrethroid compounds which are known to be insecticidally active such as cypermethrin, cyhalothrin, cyfluthrin, permethrin or the like;

2) pyrethroid-type compounds which are known to be insecticidally active such as ethofenprox, silafluofen, or the like;

3) recombinant nucleopolyhedroviruses capable of expressing an insect toxin, preferably an insect neurotoxin such as Androctonus australis insect toxin (AaIT), for example HzNPV-AaIT;

4) organophosphate compounds which are known to be insecticidally active such as profenofos, acephate, sulprofos, malathion, diazinon, methyl parathion, terbufos, or the like;

5) carbamate compounds which are known to be insecticidally active such as methomyl, thiodicarb, fenothiocarb, or the like;

6) formamidine compounds which are known to be insecticidally active such as amitraz, chlordimeform, chlorfenamidine, or the like;

7) macrocyclic lactone compounds which are known to be insecticidally active such as spinosad, avermectin, emamectin, milbemectin, nemadectin, moxidectin or the like;

8) amidinohydrazone compounds which are known to be insecticidally active such as hydramethylnon;

9) GABA antagonist compounds which are known to be insecticidally effective such as fipronil, endosulfan, or the like;

10) acetylcholine receptor ligand compounds which are known to be insecticidally effective such as imidacloprid, acetamiprid, nitenpyram, thiamethoxam, or the like.

Descriptions of the above-listed commercially available compounds may be found in The Pesticide Manual, 11th Edition, British Crop Protection Council (1997) among other publications. Descriptions of recombinant nucleopolyhedroviruses capable of expressing an insect toxin include Treacy et al, Proceedings Beltwide Cotton Conference (1999), pp 1076-1083.

Preferred compositions of the invention are those compositions having a neuronal sodium channel antagonist compound of formula I or formula III in combination with one or more compounds selected from Group A.

More preferred compositions of the invention are those compositions having a formula I or formula III compound wherein W is O; X is trifluoromethoxy and is in the 4-position; Y is trifluoromethyl and is in the 3-position; Z is CN and is in the 4-position; A is CH₂; n is 0; m, p and g are each independently 1; R and R₁ are each independently H; Z′ is Cl; R₃₃ and G are each independently CO₂CH₃; Q is p-(trifluoromethoxy)phenyl; and the dotted line configuration

represents a double bond in combination with one or more compounds selected from Group A.

Each of the compounds of formula I, II, III, IV and V embody asymmetric centers which may be represented in the stereoisomeric R-form or S-form. The present invention also includes the R-form, the S-form or mixtures comprising the R-form and the S-form in an arbitrary ratio. For compounds of formula III, the S-form is preferred.

Advantageously, the neuronal sodium-channel antagonist compound of formula I, II, III, IV or V or a mixture thereof may be formulated with a second insecticidally effective ingredient and optionally other customary formulation adjuvants. Said formulation may be dispersed in a solid or liquid diluent for application to the insect, its food supply, breeding ground or habitat as a dilute spray or as a solid dust or dust concentrate.

The active ingredients of the inventive composition may also be formulated separately as a wettable powder, emulsifiable concentrate, aqueous or liquid flowable, suspension concentrate or any one of the conventional formulations used for insect control agents and tank-mixed in the field with water or other inexpensive liquid for application as a liquid spray mixture. The separately formulated compositions may also be applied sequentially.

Advantageously, the composition of the invention may be formulated as a bait composition comprising a synergistically effective amount of a combination of a neuronal sodium channel antagonist plus one or more compounds selected from Group A and a solid or liquid edible nutritive substance. A preferred bait composition may contain by weight about 0.01% to 20% active ingredients, preferably a neuronal sodium channel antagonist in combination with hydramethylnon.

In actual practice, the composition of the invention may be applied to the plant foliage or plant stem or to the insect habitat or to the locus of a hygienic pest as a dilute spray prepared from any of the above-said formulations. The ratio of the essential active ingredients of the composition of the invention is about 1 weight part of a neuronal sodium channel antagonist to about 0.01-100 weight parts of one or more compounds selected from Group A.

The compositions of the invention are superior insecticidal compositions and are especially useful for the control of agrohorticultural pests, hygienic pests or wood-eating pests. Said compositions are highly effective for the protection of growing and harvested plants including: leguminous crops such as soybeans, snap beans, peas, wax beans and the like as well as cotton, forage crops, cole crops, leafy vegetables, tobacco, hops, tomatoes, potatoes, flowering ornamentals such as chrysanthemums, vine crops such as grapes, squash, pumpkin or melon and fruit trees such as cherry, peach, apple or citrus, from the ravages of insects.

The synergistic insecticidal composition of the invention is found to be highly active against a wide variety of lepidopteran and coleopteran insects such as Helicoverpa zea (cotton bollworm), Heliothis virescens (tobacco budworm), Leptinotarsa decemlineata (Colorado potato beetle), Diabrotica spp. (corn rootworm) and the like.

Beneficially, the composition of the invention may be useful for the prevention and control of hygienic or public health pests such as: Diptera, e.g. houseflies, mosquitoes, or the like; Hymenoptera, e.g. ants, parasitic wasps, wasps or the like; Blattaria, e.g. cockroaches; or the like.

Further, the compositions of the invention may be particularly useful for the prevention and control of wood-eating insects such as termites (Isoptera), carpenter ants (Hymenoptera), wood-destroying beetles (Coleoptera) or the like.

These and other advantages of the invention may become more apparent from the examples set forth herein below. These examples are provided merely as illustrations of the invention and are not intended to be construed as a limitation thereof.

EXAMPLE 1 Evaluation of the Synergistic Insecticidal Effect of a Combination of a Neuronal Sodium Channel Antagonist Plus a Second Insecticide

In this evaluation, Heliothis zea (cotton bollworm), Heliothis virescens (tobacco budworm) and pyrethroid-resistant Heliothis virescens larvae used are obtained from laboratory colonies. Pyrethroid-resistant H. virescens are derived from the PEG-strain [Campannola & Plapp, Proceedings of Beltwide Cotton Conference (1988)].

Cotton leaves are immersed in 1:1 v/v, acetone/water solutions of test compound, or solutions of a combination of test compounds for a period of about 3 seconds. Following immersion, leaves are allowed to air-dry for 2-3 hours. Plastic bioassay trays containing multiple open-faced wells (4.0×4.0×2.5 cm) are used as the test arenas. Cut portions of a treated leaf, a moistened cotton dental wick and a single third-instars larva are placed into each well, covered with an adhesive vented clear plastic sheet and held under constant fluorescent light at about 27° C. for a predetermined period of time. Larval mortality/morbidity is evaluated at 5 days after treatment. All treatments are replicated 4-5 fold in a randomized complete block design with 16-32 larvae per treatment. Using conventional log-probity analysis, the LC₅₀ of each treatment is determined.

Using the above protocol, a neuronal sodium channel antagonist (Compound A) may be evaluated alone at dose rates of 0.1 pap, 1.0 pap and 10.0 pap and in combination with 1.0 pap of a second insecticidal compound. Treatments which may be used are shown in Table I.

TABLE I Second Dose Compound A¹ Active Rate Dose Rate Compound (ppm) (ppm) (ppm) (ppm) (ppm) cypermethrin 0 0 0.1 1.0 10.0 1.0 0 0.1 1.0 10.0 amitraz 0 0 0.1 1.0 10.0 1.0 0 0.1 1.0 10.0 fipronil 0 0 0.1 1.0 10.0 1.0 0 0.1 1.0 10.0 acetamiprid 0 0 0.1 1.0 10.0 1.0 0 0.1 1.0 10.0 spinosad 0 0 0.1 1.0 10.0 1.0 0 0.1 1.0 10.0 thiodicarb 0 0 0.1 1.0 10.0 1.0 0 0.1 1.0 10.0 ¹Compound A = formula Ia neuronal sodium channel antagonist

EXAMPLE 2 Evaluation of the Synergistic Insecticidal Effect of a Combination of a Neuronal Sodium Channel Antagonist Plus an Amidinohydrazone

In this evaluation, adult male German cockroaches (Blattella germanica) are used. For each test, a 4.0 g portion of ground Purina Dog Chow (Hi-Pro Glob®) is treated with an acetone solution of test compound alone or in combination with a second test compound. After treatment, the acetone is evaporated and the treated dog chow is placed in a ¾ oz plastic cup which is placed in a harborage made of folded sheets of blotter paper placed in a plastic box (16″ L×11″ W×6″ H). The plastic box (test arena) is also fitted with a 1 oz narrow mouth bottle with 2 dental wicks inserted at the mouth. A control box is prepared in the same manner using ground dog chow which has been treated with reagent grade acetone. Each treatment is replicated three times. Into each test arena are placed 20 healthy adult male cockroaches which have been reared in an insectary. The test arenas are then stored at 76° F. and mortality is determined daily by visual examination. The data obtained are shown in Table 11.

TABLE II % Mortality Test % Active Days After Treatment Compound Ingredient 3 4 5 6 7 8 A¹ 0.05 0 0 0 0 0 0 A  0.10 1.7 11.7 11.7 11.7 18.3 18.3 A  0.50 5.0 5.0 5.0 5.0 5.0 5.0 B² 1.00 0 5.0 28.3 71.7 90.0 93.3 A + B 0.05 + 1.0 0 20.0 41.7 81.7 95.0 98.3 A + B 0.10 + 1.0 0 21.7 51.7 88.3 95.0 95.0 A + B 0.50 + 1.0 16.7 58.3 80.0 95.0 98.3 100.0 Control 0   0 1 .7 3.3 3.3 3.3 5.0 ¹Compound A = formula Ia neuronal sodium channel antagonist ²Compound B = hydramethylnon

As can be seen from the data shown in Table II, combinations of a neuronal sodium channel antagonist plus an amidinohydrazone insecticide demonstrate synergistic insect control.

EXAMPLE 3 Evaluation of the Synergistic Insecticidal Effect of a Combination of a Neuronal Sodium Channel Antagonist Plus a Recombinant Nucleopolyhedrovirus Capable of Expressing an Insect Toxin

In this evaluation, Helicoverpa zea (cotton bollworm) larvae are obtained from a laboratory colony. Test compounds are dissolved in 1:1 v/v acetone/water. Plastic bioassay trays (C-D International, Pitman, N.J.) are used as test arenas. Each tray contains 32 open-faced wells, 4.0×4.0×2.5 cm. A portion (5 ml) of a wheat germ-soybean flour-based artificial diet (Southland Products, Lake Village, Ark.) is poured into each well. After the diet hardened, 0.4 ml of test solution is pipetted onto the diet surface in each well. Test solutions are evenly spread over surfaces of diet by picking up the tray and gently tilting it from side to side. Trays are then held in a vented area for about 2 h, until water is no longer pooled on diet surfaces. A single 4-day-old H. zea larva is then placed on the surface of diet in each well. After larval infestation, each well is covered with an adhesive, vented, clear plastic sheet.

All test arenas are held under constant fluorescent light and a temperature of about 27° C. for duration of the assay. Larval mortality is determined at 2, 3, 4 and 7 days after treatment. A larva was considered to be dead if it exhibited little to no movement, even after being shaken in the diet tray. A total of 32 insects were tested for each treatment. The data obtained are shown in Table III.

TABLE III Conc. of % Mortality Test Active Days After Treatment Compound Ingredient 2 3 4 7 A¹ 0.1 ppm 43.8 46.9 53.1 53.1 B² 1000 OB³/ml 3.1 34.4 50.5 62.5 B  500 OB/ml 0.0 9.4 18.8 40.6 B  100 OB/ml 3.1 3.1 3.1 15.6 A + B  0.1 + 1000 87.5 90.6 93.8 96.9 A + B 0.1 + 500 75.0 78.1 84.4 87.5 A + B 0.1 + 100 62.5 75.0 75.0 78.1 Control 0 3.1 3.1 3.1 3.1 ¹Compound A = formula Ia neuronal sodium channel antagonist ²Compound B = HzNPV-AaIT, Helicoverpa zea Nucleopolyhedrovirus which expresses Androctonus australis insect toxin ³OB = viral occlusion bodies

As can be seen from the data shown in Table III, combinations of a neuronal sodium channel antagonist plus a recombinant nucleopolyhedrovirus which is capable of expressing an insect toxin demonstrate synergistic insect control. 

1. A synergistic insecticidal composition comprising a synergistically effective amount of a neuronal sodium channel antagonist in combination with one or more formamidine compounds, wherein the neuronal sodium channel antagonist is a compound of formula (I)

wherein A is CR₄R₅ or NR₆; W is O or S; X, Y and Z, are each independently H; halogen; OH; CN; NO₂; C₁-C₆alkyl optionally substituted with one or more halogen, C₁-C₃alkoxy, C₁-C₃haloalkoxy, C₃-C₆cycloalkyl, C₂-C₆alkenyloxy or sulfonyloxy groups; C₁-C₆alkoxy optionally substituted with one or more halogen, C₁-C₃alkoxy or C₃-C₆cycloalkyl groups; C₁-C₆alkoxycarbonyl, C₃-C₆cycloalkylcarbonyloxy, phenyl optionally substituted with one or more halogen, C₁-C₄alkyl, or C₁-C₄alkoxy groups; aminocarbonyloxy optionally substituted with one or more C₁-C₃alkyl groups; C₁-C₆alkoxycarbonyloxy; C₁-C₆alkylsulfonyloxy; C₂-C₆alkenyl; or NR₁₂R₁₃; m, p and q are each independently an integer of 1, 2, 3, 4, or 5; n is an integer of 0, 1 or 2; R, R₁, R₂, R₃, R₄and R₅ are each independently H or C₁-C₄alkyl; R₆ is H, C₁-C₆alkyl, C₁-C₆haloalkyl, C₁-C₆alkoxyalkyl, C₁-C₆alkoxy, C₁-C₆haloalkoxy, C₂-C₆alkenyl, C₂-C₆alkynyl, C₁-C₆alkylcarbonyl, C₁-C₆alkoxycarbonyl, C₁-C₆alkylthio, or C₁-C₆haloalkylthio; R₁₂ and R₁₃ are each independently H or C₁-C₆alkyl; and the dotted line configuration

 represents a double bond or a single bond; or a stereoisomer thereof.
 2. The composition according to claim 1 wherein the dotted line configuration

 represents a double bond.
 3. The composition according to claim 2 wherein W is O; X is trifluoromethoxy and is in the 4-position; Y is trifluoromethyl and is in the 3-position; Z is CN and is in the 4-position; A is CH₂; n is 0; m, p and q are each 1; R and R₁ are each independently H.
 4. The composition according to claim 3 wherein the one or more formamidine compounds are selected from the group consisting of amitraz, chlordimeform and chlorfenamidine.
 5. The composition according to claim 1 wherein the one or more formamidine compounds are selected from the group consisting of amitraz, chlordimeform and chlorfenamidine.
 6. A method for synergistic insect control which comprises contacting said insects with a synergistically effective amount of a neuronal sodium channel antagonist in combination with one or more insecticidally active formamidine compounds, wherein the neuronal sodium channel antagonist is a compound of formula (I)

wherein A is CR₄R₅ or NR₆; W is O or S; X, Y and Z, are each independently H; halogen; OH; CN; NO₂; C₁-C₆alkyl optionally substituted with one or more halogen, C₁-C₃alkoxy, C₁-C₃haloalkoxy, C₃-C₆cycloalkyl, C₂-C₆alkenyloxy or sulfonyloxy groups; C₁-C₆alkoxy optionally substituted with one or more halogen, C₁-C₃alkoxy or C₃-C₆cycloalkyl groups; C₁-C₆alkoxycarbonyl, C₃-C₆cycloalkylcarbonyloxy, phenyl optionally substituted with one or more halogen, C₁-C₄alkyl, or C₁-C₄alkoxy groups; aminocarbonyloxy optionally substituted with one or more C₁-C₃alkyl groups; C₁-C₆alkoxycarbonyloxy; C₁-C₆alkylsulfonyloxy; C₂-C₆alkenyl; or NR₁₂R₁₃; m, p and q are each independently an integer of 1, 2, 3, 4, or 5; n is an integer of 0, 1 or 2; R, R₁, R₂, R₃, R₄and R₅ are each independently H or C₁-C₄alkyl; R₆ is H, C₁-C₆alkyl, C₁-C₆haloalkyl, C₁-C₆alkoxyalkyl, C₁-C₆alkoxy, C₁-C₆haloalkoxy, C₂-C₆alkenyl, C₂-C₆alkynyl, C₁-C₆alkylcarbonyl, C₁-C₆alkoxycarbonyl, C₁-C₆alkylthio, or C₁-C₆haloalkylthio; R₁₂ and R₁₃ are each independently H or C₁-C₆alkyl; and the dotted line configuration

 represents a double bond or a single bond; or a stereoisomer thereof.
 7. The method according to claim 6, wherein the dotted line configuration

 represents a double bond.
 8. The method according to claim 7, wherein W is O; X is trifluoromethoxy and is in the 4-position; Y is trifluoromethyl and is in the 3-position; Z is CN and is in the 4-position; A is CH₂; n is 0; m, p and q are each 1; R and R₁ are each independently H.
 9. The method according to claim 8, wherein the one or more formamidine compounds are selected from the group consisting of amitraz, chlordimeform and chlorfenamidine.
 10. The method according to claim 6, wherein the one or more formamidine compounds are selected from the group consisting of amitraz, chlordimeform and chlorfenamidine.
 11. The method according to claim 6, wherein the insect is selected from the group consisting of Blattaria, Isoptera, Diptera, and Hymenoptera.
 12. The method according to claim 6, wherein the insects are lepidoptera or coleoptera.
 13. A method for protecting a plant from infestation and attack by insects which comprises applying to the foliage or stem of said plant a synergistically effective amount of a composition according to claim
 1. 14. The method according to claim 13, wherein the dotted line configuration

 represents a double bond; W is O; X is trifluoromethoxy and is in the 4-position; Y is trifluoromethyl and is in the 3-position; Z is CN and is in the 4-position; A is CH₂; n is 0; m, p and q are each 1; R and R₁ are each independently H.
 15. The method according to claim 14, wherein the one or more formamidine compounds are selected from the group consisting of amitraz, chlordimeform and chlorfenamidine.
 16. The method according to claim 13, wherein the one or more formamidine compounds are selected from the group consisting of amitraz, chlordimeform and chlorfenamidine. 